The term "asphalt" or "asphalt cement" as used in the description of the present application refers to any of a variety of solid or semi-solid materials at room temperature which gradually liquify when heated, and in which the predominant constituents are naturally occurring bitumens of which are obtained as residue in petroleum refining. Asphalt is further defined by Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 3, Third Ed. (1978) pp. 284-327, John Wiley & Sons, New York. An additional discussion appears in the publication entitled "A Brief Introduction to Asphalt and Some of its Uses", Manual Series No. 5 (MS-5), The Asphalt Institute, 7th Ed., September, 1974. Both of these references are hereby incorporated by reference.
Asphalt cements have found particular utility when combined with aggregates. Such combinations, generally referred to as "asphalt concrete", are employed extensively as paving compositions for roads, roofs, driveways, parking lots, airport runways, etc. The asphalt is converted to a fluid state when paving a road. One fluid form is the suspension or emulsion of the asphalt in water. After spreading and compressing the aggregate-containing asphalt, water evaporates or separates, and the asphalt hardens into a continuous mass. Another form of asphalt employed in road construction is a cutback, i.e., a liquid petroleum product produced by fluxing an asphaltic base with a suitable organic solvent or distillate. A road is formed by paving the aggregate-containing cutback and evaporating the volatile distillate from the mass. An advantage of using the above road construction techniques is the avoidance of high temperature application. In an alternative and most widely used technique, the asphalt and aggregate can be mixed and applied at elevated temperatures at the fluid state of the asphalt to form the road. This form of asphalt, which is neither cut-back nor emulsified generally is referred to as asphalt cement.
The degree and rate of hardening of asphalt cement during application and while in service ("age hardening") are factors affecting the durability of a surface such as a road pavement. A certain amount of hardening of a freshly applied surface is often desirable in order to allow the newly placed surface to be placed into service quickly. However, excessive hardening and loss of ductility of an asphalt based surface can dramatically reduce its useful lifetime. Januszke, in "Industrial Engineering Chemistry Product Research and Development", Vol. 10, (1971), 209-213, indicates that lead and zinc diethyldithiocarbamates were effective in inhibiting the adverse hardening.
In certain geographic areas, such as desert regions in the western and southwestern United States, deterioration of an asphalt road may occur quickly and is often extensive. Embrittlement and cracking of the road surface often result.
Because of the high demand for better quality materials for roofs and for the pavement of roads, airfields and other applications, there have been many suggestions in the art for producing improved asphaltic compositions.
It is known in the art that excessive age hardening of paving asphalts can be reduced through the use of certain antioxidants such as lead or zinc dithiocarbamates. The above-mentioned reference by Januszke discusses an evaluation of the effect of 24 antioxidants on paving asphalt durability and is incorporated by reference for its teachings regarding the problem and methods of assessing the performance of additives.
U.S. Pat. No. 3,992,340 describes vulcanized molding compositions based on bitumen, olefin polymers and sulfur that have utility as additives to asphalt and asphalt mixtures in order to increase the ductility of these materials.
U.S. Pat. No. 3,634,293 describes compositions containing bitumen, olefin polymers, a basic substance and sulfur. These compositions are useful as sealing compounds and for the production of sheeting and film.
It has also been suggested, for example, that the softening point of asphalt can be increased by incorporating into the asphalt a liquid polyolefin oil. In U.S. Pat. No. 3,703,393, a method is described for increasing the softening point and increasing the penetration of an air-blown asphalt by mixing the asphalt with a liquid polyolefin oil having an average molecular weight of 500-2000.
U.S. Pat. No. 4,166,049 describes a process of providing a rubberized asphalt from reclaimed rubber produced from whole scrap tires suitable for use in road and highway construction.